1. Field of the Invention
The invention relates in general to protective relay apparatus for electrical power systems, and more specifically to protective relay apparatus for detecting and clearing high impendance faults on a polyphase distribution circuit.
2. Description of the Prior Art
A low impedance fault on a polyphase distribution circuit is detected by conventional overcurrent relay techniques, with the fault being quickly isolated by tripping the proper circuit breaker or circuit breakers. A high impedance fault, however, such as might be caused by a broken or fallen conductor which does not result in a ground fault condition, will not be detected by the overcurrent relay apparatus. It would be desirable to provide a new and improved protective relay system which will detect and clear such high impedance faults. However, the more sensitive ground fault protection must not result in undesired tripping due to normal unbalanced load currents.